Method of preparing alkali metals and alkaline earth metals



March 1931- J. H. DE BOER 1,797,131

METHOD PREPARING ALKALI METALS AND ALKALINE EARTH METALS Filed May 6, 1929 .l'nuenfor: defioer,

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Patented Mar. 17, 1931 JAN HENDRIX DE BOER, 0F EINDHOVEN, NETHERLANDS, ASSIGNOR TO N. PHILIPS GLOEILAMPENFABRIEKEN, OF EINDHOVEN, NETHERLANDS, A LIMITED LIABILITY coMPA nY on THE NETHERLANDS METHOD PREPARING ALKALI METALS AND ALKALINE EARTH METALS "Application filed May 6, 1929, Serial No. 360,993, and in the Netherlands July 4, 1928.

This inventon relates to a process of preparing alkali metals and alkaline-earth -metals by the reduction of one or more compounds of these metals.

According to the invention, a metalbelonging to the first sub-group of the fourth principal group of the periodic system is utilized for the reduction of alkaliand alkalineearth metal compounds. This reduction may be effected by heating one or more of these metals, which preferably should be present in excess, in a vacuum or in an inert gas together with one .or more of the said compounds, these compounds being preferably so chosen that the compounds of the reducing metal which are produced by the reduction, are not or slightly volatile at the reaction temperature. According to theinvention, a

powdered mixture of the reactive substancesmay be heated, if desired, after being first brought into a coherent form, for instance, that of small rods or pastils.

The process is especially suited for the reduction of caesium compounds.

Zirconium is conveniently used as the reducin metal and non-hygroscopic salts of the allrali metals and alkaline-earth metals such as caesium sulfate, are very suitable for being reduced with the aid of the process according to the invention although the invention is not restricted at all to that kind of compound.

The invention is of great importance in the manufacture of electric discharge tubes. Such tubes often contain alkalior alkalineearth metals either in a metallic form or in compounds, for example, oxides. Various methods of introducing these metals into electric discharge tubes are known but the known methods often have the disadvantage that at the same time undesirable or harmful substances are brought into the tube. The method according to the invention has not this disadvantage.

A mode of carrying out the process according to the invention, which is particularly suitable for usein the manufacture of discharge tubes, consists in heating a capsule which contains one or more of the alkali and alkaline-earth metal compounds that are to be reduced and whose wall, which has one or more apertures, consists entirely or pjartly of a metal belonging to the first sub-groupfofthe fourth principal group of the periodic system. The heatin of this capsule may take place in the tu e itself andmay even occur after the electrodes havebeen freed of occluded gases.

Another example of carrying out the process according to the invention will be hereinafter described with reference to the accompanying drawing, wherein Fig. 1 is a view partly in elevation and if partly in section of an apparatus for carrying out my invention;

r Fig. 2 is an elevation of the same device, rotated 90 about both its horizontal and its vertical axes; while Fig. 3 is a fragmentary ratus 3. In the preferred instance, this apparatus comprises four horizontal arms, two of which are-indicated in Fig. 1 by the reference numeral 4, and each arm being provided by vertical side tubes 5. In the center of these arms the apparatus communicates with a vacuum pump by means such as a tube 6, preferably provided with a narrow portion 8.

A powdered mixture 7 is placed in the quartz tube, and this mixture preferably comprises an alkali or alkaline earth metal compound, such for instance as caesium chloride, and a metal belonging to the first subgroup of the fourth principal group of the periodic system, such for instance as zirconium. In lieu of the foregoing powdered mixture, it is quite feasible to produce a mixture in a coherent form, that is, small rods or pastils; should these rods or 'pastils be employed, it is preferable to use non-hygroscopic salts. A third form of the mixture com rises a zirconium boat or capsule, an alkali or alkaline metal earth compound, which may be barium iii" oxide; while still a fourth method, which permits the obtention of the reaction materials in the tube, comprises stretching a zirconium wire in the quartz tube, after having previously immersed the wire in a. molten alkali or alkaline earth metal compound such as a molten hydroxide. It is obvious that with the several methods of employing the reaction mixture, there are also different methods of heating the same. When a re action mixture has either the above mentioned powdered or coherent form, it is desirable to heat the same by means of an outlet of the tube fitted as a furnace, or by means of eddy currents induced by 'a high frequency magnetic field. This last method of heating is the most desirable should the "third form of reaction mixture beemployed. In the fourth method, that in which the zirconium wire is cmployed, the heating can best be carried out by means of an electric current caused to traverse the'said wire. In the example illustrated, and after the reaction mixture is introduced in say, powdered form, in the quartz tube, the apparatus is first evacuated while being heated at a temperature of approximately 400 (1., by placing the whole apparatus in a furnace. Thereafter the tube is removed from the fur nace and is heated by means of a smaller furnace to a temperature of approximately 800-1000 (3.; the reaction then takes place and the alkali or alkaline earth metal such as caesium evaporates and precipitates on the glass wall at B. The reaction having been nished, the apparatus is melted off at the narrow portion 8 and is turned through 90 into the position indicated in Fig. 2. The caesium precipitated at B is now heated by suitable means such as a gas burner and the metal is distilled into the tubes 5. These tubes are melted off and tubes are produced containing pure caesium, as illustrated in Fig. 3. These tubes can be used for a variety of purposes and may be connected to any appa ratus in which an alkali or alkaline earth metal is to be em loyed. In such cases the neck 10 of the tu e 5 can be readily broken and the metal can be distilled in the apparatus on which these tubes are connected and in which the alkali is to be employed.

The temperature at which the reactions take place is not the same for all cases but depends on different circumstances, inter alia, on the pressure within the reaction vessel, on the nature of the metals and compounds used and on the mixing proportion. This temperature generally amounts to around about 600 C., but may also be less, which may appear from some examples hereinafter to be given. When heating one part of caesium sulfate together With ten parts of zicronium in the form of a pressed rod to a temperature above 500 (1, one observes a slow generating of caesium, which is the more intense as the temperature increases. Even when the temperature is raised to about 800 sulfates can also be converted either by a cofitmuousymcess or under exploslve C11- cumstances witlTthe*aid QflJlm PL S ccording to the invention. When one starts with caesium bichromate and zicronium inthe proportion 1: 4, an explosive reaction occurs already at 300 (1, whereby for exam le 48% of the caesium may be liberated. If t e mixing proportion is 1: 20, the reduction practically does not set in until at about 500 (3., and the reaction proceeds calmly. Caesium bisulfate can also be reduced by explosion already at 300 C., even 97% of the caesium bein liberated in that case from the mixture. mpared with the known methods of introducing metals such as barium, caesium, rubidium and the like into discharge tubes, the application of the process according to the .invention afiords many advantages. Thus, for example it lacks the laboriousness of the known methods in which az'ides are caused to decompose and more particularlyit favourably distinguished itself therefrom in that the products formed in the new process, are frequently not volatile so that special meas-' ures for removing them from the discharge tube can be dispensed with. Applied to discharge tubes the process presents the additional advantage that the reducing metals which may be present in excess, act as getters and consequently absorb and thus render harmless any undesired gases which after exhaustion of the tube might still .be present or be generated therein. The alkali and alkaline earth metals formed in a discharge tube by this process and which, for example, precipitate on the wall show in a high measure a getter action and compared with the magnesium generally used for this purpose,

they afford the advantage of having a higher evaporation temperature than the said metal. In fact, magnesium mostly begins to evaporate already before the gases occluded in the metal parts of the tube are expelled therel, from to a suflicient extent. The presence of inert gases such as rare gases, with which 1 discharge tubes are often filled does not impede the above described reactions provided the pressure is not too high.

What I claim is:

1. A process of preparing alkali metals and alkaline earth metals, which consists in heating a compound of the said metals in con tact with a reducing agent, said reducing 75 the mixture is set free. Bichromates and b1- 4 porizing temperature higher thanthe reaction temperature.

2. A process ofvpreparing alkali metals and alkaline earth metals, which comprises introducing into a container a compound of the metal to be prepared in contact with a metal belonging to the first subgroup of the 4th column of the periodic system, evacuating the container and heating the said substances to a temperature to cause the chemical reaction between them, a compound being used which forms with the metal ofthe said subgroup aproduct having a vapor izing temperature higher than the reactive temperature.

3. A process of preparing alkali metals and alkaline earth metals, which consists in heating in an evacuated container a powdered mixture, comprising a compound of the metal to be prepared and a metal belonging to th'e'first subgroup of the 4th column of the'periodic system, to a temperature to cause a chemical reaction between the constituent substances of the said mixture, a compound of the metal to be prepared being used having a vaporizing temperature higher than the reacting temperature.

4. A process of preparing alkali metals and alkaline earth metals consisting in heating in an evacuated container a pastil prepared from a owdered mixture comprising a compound of the metal to be prepared and a metal belongin to the first subgroup of the 4th column oi? the periodic system, to a temperature to cause a chemical reaction between the constitueut substances of the pastil, a compound of the metal to be prepared being used, having a vaporizing temperature higher than the reacting temperature.

5. A process of preparing alkali metals and alkaline earth metals consisting in introducing into an evacuated container a metal capsule, enclosing a compound of the metal to be prepared, said capsule consisting of a metal'belonging to the first subgroup of the fourth column of the periodic system, and heating the said capsule to a temperature to cause a chemical reaction between its wall and its content.

6. A process of preparing alkali metals and alkaline earth metals, which consists in heating in an evacuated container a nonhygroscopic salt of the metal to be prepared in contact with zirconium to a temperature to cause a chemical reaction between the said substances, a salt of the metal to be prepared being used, which forms with zirconium a product having a vaporizing temperature higher than the reaction temperature.

7. A process of preparing metallic'caesium,

which consists in heating in an evacuated container a non-hygroscopic salt of caesium in contact'with zirconium to a temperature lying between 300 and 800 C.

8. A process of preparing metallic caesium,

which consists in heating in an evacuated container a mixture of caesium sulphate and zirconium to a temperature lying between 300 and 800 C.

9. A process of preparing metallic caesium, which consists in heating in an evacuated container a mixture containing caesium sulphate and zirconium in a proportion of about 1:4 to a temperature of about 500 C.

In testimony whereof I have signed my nameto this specification.

JAN HENDRIK DE BOER. 

